Respiration 3 Flashcards by Sophie Chung

What division of the nervous system normally initiates and controls breathing?

Autonomic NS

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What happens during normal expiration?

Respiratory muscles relax

Lungs empty primarily through elastic recoil

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What type of muscles are the respiratory muscles?

Skeletal

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What type of neuron stimulates the respiratory muscles?

α-motor neurons

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What is the main respiratory muscle and what stimulates it?

Diaphragm

Two branches of phrenic nerve (C3-5)

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What innervates the intercostal muscles?

Segmental spinal nerves (intercostal nerves)

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Where is the basic rhythmicity of breathing generated?

Brainstem - primarily medulla oblongata

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What is the medullary respiratory centre also referred to as?

Respiratory rhythm generator

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What do the dorsal respiratory groups do?

Contain inspiratory neurons which demonstrate rhythmic activity and stimulate inspiratory muscles

Receives afferent/sensory inputs from lung receptors via vagus nerve

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What do the ventral respiratory groups do?

Contain neurons with a degree of spontaneous rhythmic electrical pacemaker activity

Inspiratory and expiratory neurons

Receives inputs from dorsal respiratory group and central chemoreceptors

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Describe the processes in normal quiet breathing.

Pacemaker neurons stimulate inspiratory neurons causing inspiratory muscle contraction

Expiration is mostly passive recoil - minimal expiratory neuron activity

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Describe the processes in breathing during exercise.

Pacemaker neurons stimulate inspiratory neurons causing inspiratory muscle contraction

Other inputs stimulate expiratory neurons causing expiratory muscle contraction

Alternate stimulation/mutual inhibition of inspiratory and expiratory neurons

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What is the general function of the pons?

Receive inputs from cerebrum and hypothalamus and feed them into the medullary respiratory centre

Fine tuning of rhythmicity

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What are the two parts of the pons involved in breathing?

Pneumotaxic centre

Apneustic centre

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What is the function of the pneumotaxic centre?

Smooths transitions between inspiration and expiration by regulating apneustic centre and dorsal respiratory group

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What is the function of the apneustic centre?

Stimulates the dorsal respiratory group to promote inspiration and increase breath duration

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What is the function of the hypothalamus and limbic system?

Mediate response to changes in temperature and emotional state (involuntary)

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How can voluntary control override the respiratory centre?

Motor neurons in cerebral cortex connect directly to motor nerves supplying respiratory muscles and bypass medulla

Why is voluntary control of breathing important?

Speech, eating, diving…

Back-up mechanism in case respiratory centre fails

Which receptors are involved in the Hering-Breuer inflation reflex?

Lung stretch receptors

Describe the Hering-Breuer inflation reflex.

Inspiration stretches airways which activates the stretch receptors in bronchial smooth muscle (primarily bronchioles)

Vagus nerve sends impulses to dorsal respiratory group which inhibits inspiratory neurons

Further inspiration inhibited, giving time for expiration

When is the Hering-Breuer inflation reflex important?

When tidal volume is high (eg. exercise)

Describe how irritant chemicals/smoke/dust affect breathing.

Activate lung irritant receptors between epithelial cells

Vagus nerve sends impulses to medulla

Stimulates coughing and bronchoconstriction

Describe the process which occurs during long-term quiet breathing.

Slow collapse of lungs activates lung irritant receptors

Vagus nerve sends impulses to medulla

Surfactant release stimulated

Deep augmented breaths every 5-20 minutes

Prevents slow collapse of lungs

How can anxiety cause respiratory alkalosis?

Hyperventilation lowers arterial partial pressure of carbon dioxide/causes hypocapnia

What can hypocapnia cause?

Cerebral vasoconstriction which decreases amount of blood going to brain Cerebral hypoxia and dizziness

What can hypercapnia cause?

Flushing/peripheral vasodilatation (Severe hypercapnia) depressed CNS function

What are the arterial partial pressures of oxygen and carbon dioxide?

Oxygen = 12.5kPa Carbon dioxide = 5.3kPa

How does alveolar partial pressure of carbon dioxide affect ventilation?

Mostly linear relationship - small increase = large increase in ventilation Below 5.3kPa = basal rhythm of respiratory centre prevents no breathing at all Very high alveolar pp - depression of respiratory centre as further increases in ventilation will be counter productive (produce more CO2)

What is the major drive of respiration?

Partial pressure of carbon dioxide

How does metabolic acidosis affect the ventilation-pCO2 graph and why?

Leftward shift - increased ventilation Chemoreceptors become more sensitive to carbon dioxide Same pp of carbon dioxide will produce a larger ventilatory response (x3) to increase pH normal

How does metabolic alkalosis affect the ventilation-pCO2 graph and why?

Rightward shift - decreased ventilation Chemoreceptors become less sensitive to carbon dioxide Suppressed breathing at the same pp to decrease pH to normal

What is the effect of arterial partial pressure of oxygen on ventilation (constant pp of CO2)?

Very little effect until BELOW 8kPa Below 4kPa results in depression of respiratory centre as further ventilation will be counter productive

What does the term "synergistic" mean when talking about the effects of pp of oxygen and carbon dioxide on ventilation?

When combined, they give a much greater effect on ventilation

By how much does the synergistic effect of partial pressures increase ventilation?

6 times

What are the two types of chemoreceptor?

Central chemoreceptor Peripheral chemoreceptor

Where are the central chemoreceptors located?

Ventrolateral surface of medulla, near the entry of CNX (vagus) and CNIX (glossopharyngeal)

What do the central chemoreceptors detect?

[H+] and pCO2 of cerebrospinal fluid

Which type of chemoreceptor is majorly responsible for the response to pCO2?

Central chemoreceptors

Where are the peripheral chemoreceptors located?

Carotid bodies at the top of the bifurcation of common carotid Aortic bodies on the upper part of the aortic arch

Which cranial nerves innervate the peripheral chemoreceptors?

Vagus X Glossopharyngeal IX

What do the peripheral chemoreceptors detect?

pO2, pCO2 and [H+]

Which peripheral chemoreceptors are most important in humans and why?

Those in the carotid bodies Produce very fast response to acute changes in blood gas partial pressures

How do the carotid bodies respond to decreased pO2 or increased pCO2/[H+]?

Glomus cells release dopamine onto carotid sinus nerve endings to generate action potentials Show a synergistic response to combined stimuli